The Volkswagen Golf TSI I'm driving is stopped at a crossroad intersection, its engine having shut off automatically as the brakes were applied. When it’s my turn to move, I slip my foot off the brake pedal and the 1.2-L gasoline engine fires almost telepathically, with a level of smoothness I’d expect from an Audi—a V6 Audi.
Tipping hard into the throttle, the powertrain controller calls for “E-boost” mode, as I point the Golf along the roller-coaster roads in appropriately named Auburn Hills, MI. It’s a useful location to evaluate the Golf’s prototype 48-V hybrid module, developed by Continental. Under E-boost, the Conti module provides an additional 14 kW to the otherwise stock VW powertrain, delivering stronger acceleration—for such comparisons, the demo car allows me to shut off the 48-V system and revert to the 12-V base to feel the difference.
In addition, Conti’s 48-V module offers Coasting (e-motor decoupled), Sailing (motor coupled), and steady-state operating modes along with ample brake-energy recuperation. Though not part of the demo car, the production system may include driver-modulated regen braking, potentially using fingertip control buttons on the steering wheel—a welcome and practical feature.
This is clearly one of the most polished prototype hybrid systems of the many I’ve driven, I tell my passenger Juergen Wiesenberger, who is Conti’s Director of Hybrid Electric Vehicle Engineering in North America. He replies that a contingent of powertrain management from a certain local OEM had also driven the Golf recently, and shared my opinion. I report that compared with the stock VW 12-V system, the start-up is noticeably quicker and smoother. And vs. the coarse, abrupt 12-V stop-start in the current BMW 3-Series—a system that’s been widely panned by competitor engineers and media testers alike—the prototype Conti 48-V system is in another league in terms of its overall seamlessness and functionality.
Wiesenberger revealed that a production 48-V system based on the prototype is scheduled to launch at two OEMs in the 2016 time frame, with “a number of projects” in the pipeline.
A bolt-on hybrid solution
“Years ago the industry had ‘42-V fever’ as I like to call it,” Wiesenberger said, recalling the 1990s period when it appeared that 42-V would become the new automotive electrical architecture due to rapidly increasing power demands from heated windshields, seats and steering wheels, among many other new features.
While 42-V never took off—12-V systems just got a lot more efficient—the electrical demands are greater than ever. They now include electric power steering; electric HVAC, coolant and lubricant pumps; and new chassis controls. Also in the works to reduce engine-out emissions are sophisticated electric-boosting systems, including the e-turbos Continental is developing, which also require higher voltage.
“Our OEM customers want the added electrical capability, along with lower emissions, at a lower investment,” he explained. “They’re talking dollars per gram of CO2 reduction.”
Thus the trend towards 48/12-V dual voltage systems that include mild-hybridization along with greater electric potential. Continental engineers created their 48-V module to fill the market gap between the bare-bones 12-V “micro hybrid” stop-starts and the more capable (and far more costly) 120-400-V hybrids, Wiesenberger noted. Conti’s solution is a bolt-on 48-V belt-driven starter/generator module (BSG) that’s quite package-efficient and requires no changes to the vehicle transmission, and minimal tweaks to engine calibration.
“As small as it is, the 48-V will do nearly everything the more expensive full hybrid can do,” he asserted. Indeed, the European OEMs and increasingly, the North American industry are moving forward with 48-V production programs (see http://articles.sae.org/12827/). Their functional benefits include filling in the low-rpm torque gap in smaller turbocharged engines, and delivering greater brake-energy recuperation vs. 12-V systems (typically 8 kW vs. 2 kW), which is good for a 10-13% reduction in CO2 emissions on the NEDC cycle, and 7-10% on the new WLTC cycle.
Extending the 48-V capabilities
Similar to General Motors’ production eAssist (for which Conti supplies the e-motor), the Continental 48-V system also is a P1 type mild hybrid, its designation defined by the “position 1” mounting on the front of the combustion engine. Developed in one year by a team of three engineers, its e-motor is a liquid-cooled induction machine, with integrated inverter. The unit weighs 12 kg (26 lb). The motor is rated at 5 kW permanent/13 kW peak. ContiTech supplies the reinforced drive belt, which is kept taut by a low-friction Schaeffler belt tensioner.
“The trick with the 48-V is managing the back-and-forth torque transmission,” explained Greg Goestenkors, Hybrid Systems Sales Director. “In order to transfer up to 15 kW the belt becomes a critical element. Being a BSG we can use the Schaeffler clutches to decouple the e-motor from the drive, enabling the vehicle to crawl along on electric drive alone,” such as in bumper-to-bumper traffic. “That’s a generation beyond the system in our current demo car,” he said.
The lithium-ion battery and compact dc-dc converter are located in the demo Golf’s trunk. Supplied by SK Continental E-motion, Conti’s joint-venture with battery-cell maker SK Innovation, the battery’s small size could mistake it for a 12-V unit. All in all, the 48-V module is a tidy package, its bill-of-material reduced by half compared to a previous system, due to piggybacking the power inverter on the e-motor and eliminating their connecting cables.
Future 48-V system iterations will include an integrated starter-generator (ISG) system, in which the e-motor is located in the driveline, Wiesenberger said. And his eyes lit up as he noted the synergies under development between Continental’s hybrid engineers and its electronic controls and automated-driving groups.
“We call it eHorizons—a forward-looking, predictive energy management system for not only the powertrain but for the entire vehicle,” he said. For a 48-V hybrid vehicle or the PHEV that Conti also is developing, the eHorizons would use the vehicle’s GPS and traffic data to optimize the electrical energy available via the BSG and regen braking, according to real-time driving conditions.
Using the full capability of the onboard sensors and their 3-4 mi range, the vehicle will “know” when it needs to prepare to discharge the battery for more acceleration—as when approaching a long grade—as well as preparing the battery to receive a lot of recuperated energy as the vehicle begins a long downhill descent.
“We’re also developing adaptive strategies for our PHEV, where the car ‘learns’ its position and so offers the driver the quickest route home when the battery is becoming depleted,” Wiesenberger said.